The 1961 Fender Twin Amp... The Vibrato in this amp was actually more
than Tremolo. I am not sure exactly what the effect should be called.
Vibrato? Tremolo? Modulated dual filter? Phasor? Leo called it “vibrato”
which isn’t technically correct. It is an amazing sound though!! Truly
the “sinewave” Brownface tremolo sound, folks are looking for. We used
this as the starting point adding a lot more range of speeds and much
more depth.

Like most other Catalinbread pedals, the Pareidolia
was designed for both 9v and 18v operation, the latter giving a more
pronounced up-front sound to the effect. We worked very hard tuning this
pedal, and the result is a complex modulation that is quite literally a
mesmerizing effect, where you stop thinking and just start playing. It
frees your mind to be creative. It is hypnotic, yet unlike over the top
modulation effects the Pareidolia doesn't pwn your sound, allowing your
playing to shine through. And unlike other modulation pedals it is less
picky in its placement with other pedals. Whether the Pareidolia is
placed pre-dirt, post-dirt, or sandwiched between, this pedal still
sounds great.

We're convinced that once you turn on the Harmonic
Mesmerizer, you'll have a tough time turning it off. Here's a fantastic
clip to wet your whistle, showing the Pareidolia's range both clean, and
through a cranked amp.

Your guitar signal is split into two. One feeding a
gain stage filtered to pass highs and the other filtered to pass lows.
These stages are tuned to share some common frequencies in the middle so
when it modulates they have a nice swirly soup in the midrange. The
amplitude (via bias) of each stage is modulated by a sinewave out of
phase with the other. The result of this is as one stage’s volume is
going down the other is going up. The fact that it is modulated by bias
means the phase of each stage is modulated ever so slightly. The
interaction of this slight phase shift on the shared midrange
frequencies results in some interesting subtle frequency canceling while
the amplitude goes up and down.

So what you hear is quite literally mesmerizing. Your
brain has multiple points of modulation to listen for, phase shift,
amplitude, and frequency band. When you play a held out chord your brain
hears things that is not actually happening, such as the LFO sometimes
seems to be speeding up and slowing down. In reality the LFO is staying
the same speed, but because the sound is so complex your mind is
attempting to make sense of all the variables. I liken it to seeing
faces in clouds, in wood grain, or on Mars – thus the name Pareidolia.